Display device and method of driving the same

ABSTRACT

According to one embodiment, a display device includes a display unit and a driver unit. The driver unit includes a display drive unit, a power supply unit and a control unit. The control unit instructs a display period in which the image is displayed in the display unit and a non-display period in which the image is not displayed to the display drive unit, and instructs mitigation driving which mitigates a difference in an electrical load of the display drive unit between the display period and the non-display period to the power supply unit in the non-display period.

CROSS REFERENCES TO RELATED APPLICATIONS

The present application is a continuation application of U.S. patentapplication Ser. No. 14/854,903, filed on Sep. 15, 2015, whichapplication claims priority to Japanese Priority Patent Application JP2014-187890 filed in the Japan Patent Office on Sep. 16, 2014, theentire content of which is hereby incorporated by reference.

FIELD

Embodiments described herein relate generally to a display device whichrepetitively exhibits a display period and a non-display periodperiodically, and a method of driving the same.

BACKGROUND

A mobile terminal (a smartphone, personal assistant device [PAD], tabletcomputer, etc.) includes a display device of liquid crystal, organicelectroluminescent (EL), and the like. Also, in a display device usedfor a mobile terminal, additional features, such as a touch sensor, aregenerally added.

Meanwhile, in a liquid crystal display device to which a touch sensorfunction, for example, is added, while the touch sensor is operated in ablanking period of liquid crystal driving, a panel driving load differsin a display driving period (hereinafter referred to as a displayperiod) and a sensing operation period (hereinafter referred to as anon-display period) of the touch sensor, and thus, a load variation mayoccur periodically. At this time, a booster circuit or a regulatorcircuit for the liquid crystal driving cannot catch up with the loadvariation, and thus, a ripple occurs in a power supply voltage. Theripple may produce noise due to vibration of components.

As described above, a display device which repetitively exhibits adisplay period and a non-display period entails a problem that a rippleoccurs in the power output because of a periodic load variation, and theripple may produce noise.

Hence, an object of the present embodiment is to provide a displaydevice which is capable of mitigating the load variation caused by thedisplay and non-display periodicity, thereby suppressing the ripple ofthe power output, and a method of driving the same.

SUMMARY

This application relates generally to a display device.

In an embodiment, a display device comprising a display unit configuredto display an image; and a driver unit configured to drive the displayunit, wherein the driver unit comprises a display drive unit configuredto supply power to the display unit, and to selectively drive thedisplay unit in a display state and a non-display state depending on anamount of the power supply; a power supply unit configured to supplypower to the display drive unit; and a control unit configured tocontrol the display drive unit and the power supply unit, the controlunit instructing a display period in which the image is displayed in thedisplay unit and a non-display period in which the image is notdisplayed to the display drive unit, and instructing mitigation drivingwhich mitigates a difference in an electrical load of the display driveunit between the display period and the non-display period to the powersupply unit in the non-display period.

In a further embodiment, a display drive method comprising supplyingpower to a display unit which displays an image, and selectively drivingthe display unit in a display state and a non-display state depending onan amount of the power supply, wherein a display period in which theimage is displayed in the display unit and a non-display period in whichthe image is not displayed are determined; and power is supplied in thenon-display period to mitigate a difference in an electrical load ofdisplay driving between the display period and the non-display period.

Additional features and advantages are described herein, and will beapparent from the following Detailed Description and the figures.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a perspective view showing a schematic structure of asensor-equipped display device to which one embodiment is applied.

FIG. 2 is an illustration which takes out and shows a main circuitblock, which is a part of FIG. 1.

FIG. 3 is an illustration which schematically shows the structure of afirst substrate and an equivalent circuit in a liquid crystal displaypanel.

FIG. 4 is an illustration showing an equalizing circuit of pixel PX ofFIG. 3.

FIG. 5 is a diagram showing a block configuration example inside aliquid crystal driver which is an IC chip to which one embodiment isapplied.

FIGS. 6A and 6B are illustrations each showing a configuration exampleof a power supply unit inside the liquid crystal driver of FIG. 5.

FIG. 7 is a diagram showing a configuration example of a timingcontroller inside the liquid crystal driver of FIG. 5.

FIG. 8 is a flowchart showing the specifics of control which isprocessed by a sequencer indicated in FIG. 7, as a first embodiment forreducing load variation.

FIG. 9 is a timing chart indicating the specifics of control of FIG. 8.

FIG. 10 is a flowchart showing the specifics of control which isprocessed by the sequencer indicated in FIG. 7, as a second embodimentfor reducing load variation.

FIG. 11 is a timing chart indicating the specifics of control of FIG.10.

FIG. 12 is a flowchart showing the specifics of control which isprocessed by the sequencer indicated in FIG. 7, as a third embodimentfor reducing load variation.

FIG. 13 is a timing chart indicating the specifics of control of FIG.12.

FIG. 14 is a flowchart showing the specifics of control which isprocessed by the sequencer indicated in FIG. 7, as a fourth embodimentfor reducing load variation.

FIG. 15 is a timing chart indicating the specifics of control of FIG.14.

DETAILED DESCRIPTION

Various embodiments will be described hereinafter with reference to theaccompanying drawings.

The embodiment is described below. According to this embodiment, adisplay unit configured to display an image, and a driver unitconfigured to drive the display unit are provided. The driver unitcomprises a display drive unit configured to supply power to the displayunit, and to selectively drive the display unit in a display state and anon-display state depending on an amount of the power supply, a powersupply unit configured to supply power to the display drive unit, and acontrol unit configured to control the display drive unit and the powersupply unit. The control unit instructs a display period in which theimage is displayed in the display unit and a non-display period in whichthe image is not displayed to the display drive unit, and instructsmitigation driving which mitigates a difference in an electrical load ofthe display drive unit between the display period and the non-displayperiod to the power supply unit in the non-display period.

The above structure enables load variation caused by the display andnon-display periodicity of the display device to be mitigated, therebysuppressing a ripple of a power output.

More detailed descriptions will be given referring to the drawings. FIG.1 is a configuration diagram showing the entire blocks of a mobileterminal to which one embodiment is applied.

FIG. 1 is perspective view showing a schematic structure of asensor-equipped display device DSP according to one embodiment. In FIG.1, a touch-sensor-integrated liquid crystal display panel LCD comprisesa first substrate SUB1, a second substrate SUB2 opposed to the firstsubstrate SUB1, and a liquid crystal layer formed between the firstsubstrate SUB1 and second substrate SUB2. Note that the first substrateSUB1 may be referred to as an array substrate, and the second substrateSUB2 may be referred to as a counter-substrate. A liquid crystal driverIC1 which drives the liquid crystal display panel LCD is mounted on thefirst substrate SUB1, for example. The liquid crystal driver IC1 may bereferred to as a first IC chip or a driver circuit.

The liquid crystal display panel LCD integrally comprises a capacitivetouch sensor SE, for example. In the example of the drawing, on asurface of a display area (which may also be referred to as an activearea) DA of the liquid crystal display panel LCD, a detection element(which may also be referred to as a detection electrode) Rx which formsthe touch sensor SE is provided. This type of sensor-equipped displaydevice DSP is referred to as an on-cell device. Alternatively, thedisplay device DSP may be an in-cell device in which an electrode whichforms the touch sensor SE is provided within the liquid crystal displaypanel LCD. The touch sensor SE is controlled by a touchpanel controllerIC2 (which may also be referred to as a second IC chip or a sensorcircuit).

Further, an application processor (which may also be referred to as afirst control unit) HOS is provided, and the application processor HOSis connected to the liquid crystal display panel LCD via a flexibleprinted circuit FPC1 and the liquid crystal driver IC1, and connected tothe touch sensor SE via a flexible printed circuit FPC2 and thetouchpanel controller IC2. The liquid crystal driver IC1 and touchpanelcontroller IC2 mentioned above may be structured in the same chip.

A backlight unit BL which illuminates the liquid crystal display panelLCD is disposed below the first substrate SUB1. A flexible printedcircuit FPC3 connects the backlight unit BL and the applicationprocessor HOS. As the backlight unit BL, various types of backlight unitBL are applicable, and as a light source, a product using alight-emitting diode (LED) or a backlight unit BL using a cold cathodefluorescent lamp (CCFL), etc., is available.

Although the sensor-equipped display device DSP is provided with a powersupply circuit, etc., other than a battery (a secondary battery) BATT,FIG. 1 does not illustrate such an element.

FIG. 2 takes out and shows a main circuit block, which is a part ofFIG. 1. A portion surrounded by a broken line in FIG. 2 represents thepart of the first substrate SUB1. In a non-display area of the secondsubstrate SUB2, a gate circuit GD is structured. Also, next to the gatecircuit GD, a common electrode driving circuit CD is structured.

Further, a source selection circuit (which may also be referred to as amultiplexer) MUP is structured in a lower non-display area of the secondsubstrate SUB2. The liquid crystal driver IC1 can control the gatecircuit GD and the common electrode driving circuit CD. Also, the liquidcrystal driver IC1 can write a pixel signal to a pixel (which may alsobe referred to as a display element) of the liquid crystal display panelLCD via the source selection circuit MUP. In this way, the liquidcrystal display panel LCD can set a write period with respect to a pixeland a touch detection period.

The touchpanel controller IC2 can process a touch detection signalobtained from a touch detection electrode, and obtain coordinate data ona contact position of the user's finger relative to a display surface.

The liquid crystal driver IC1 intercommunicates with the applicationprocessor HOS, and requests and receives, for example, data.

The application processor HOS can supply video data, a command, asynchronization signal, etc., to the liquid crystal driver IC1.

The application processor HOS, the liquid crystal driver IC1, and thetouchpanel controller IC2 are driven by power supply from the batteryBATT.

FIG. 3 schematically shows a part of an equivalent circuit on the firstsubstrate SUB1 of the liquid crystal display panel LCD.

The liquid crystal display panel LCD includes a display area DA in whichan image is displayed. In the first substrate SUB1, in a non-displayarea of the first substrate SUB1, the source selection circuit MUP, thegate circuit GD, the common electrode driving circuit CD, and an outerlead bonding pad group (hereinafter referred to as an OLB pad group) pG1are formed.

The liquid crystal driver IC1 is connected to the source selectioncircuit MUP, the gate circuit GD, the common electrode driving circuitCD, and the OLB pad group pG1. Although the entirety is not shown, theliquid crystal driver IC1 and the gate circuit GD are connected to eachother by a control line which outputs a panel control signal. The liquidcrystal driver IC1 can give a control signal to a control switchingelement CSW1 via the control line.

In the display area DA, pixels PX are located between the firstsubstrate SUB1 and the second substrate (not shown). The pixels PX arearrayed in an m×n matrix in a first direction X and a second direction Ywhere m and n are positive integers.

In the display area DA, n gate lines G (G1 to Gn), m source lines S (S1to Sm), common electrodes CE (C1 to Cn), etc., are formed on the firstsubstrate SUB1.

The gate lines G extend substantially linearly in the first direction X,are led out to the outside of the display area DA, and are connected tothe gate circuit GD. The gate lines G are aligned to be spaced apartfrom each other in the second direction Y. The gate lines G (G1, G2, . .. , Gn) are connected to control switching elements CSW1, respectively.

The source lines S extend substantially linearly in the second directionY, and cross the gate lines G. The source lines S are aligned to bespaced apart from each other in the first direction X. The source linesS are led out to the outside of the display area DA, and connected tothe source selection circuit MUP.

The common electrodes CE (C1, C2, . . . , Cn) extend substantiallylinearly in the first direction X, and are aligned to be spaced apartfrom each other in the second direction Y.

The common electrodes CE may be divisional electrodes bundled bymultiple electrodes (for example, three electrodes). In this case, thecommon electrodes CE (C1 to Cn) are configured as n/3 divisionalelectrodes C (C1 to Cn/3). Hereinafter, the embodiment will be describedassuming that the common electrodes CE are structured.

The common electrodes CE are led out to the outside of the display areaDA, and are connected to the common electrode driving circuit CD. Thegate lines G, the source lines S, and the common electrodes CE are notnecessarily extended linearly, but part of them may be bent.

The gate circuit GD comprises n control switching elements CSW1. Each ofn control switching elements CSW1 is selectively closed (to establish anon state) or opened (to establish an off state), so that permission orprohibition of writing a pixel signal to a corresponding pixel PX can becontrolled. Also, n control switching elements CSW1 may be concurrentlyclosed (to establish an on state) in an abnormal state (i.e., at thetime of specific control operation), for example, to allow writing of ablack level image signal, for example, in all pixels PX.

The pixel signal is sequentially written to a pixel connected to aselected gate line via the source selection circuit MUP.

FIG. 4 is an equivalent circuit diagram showing the pixel PX shown inFIG. 3. The pixel PX comprises a pixel switching element PSW, atransparent pixel electrode PE, a transparent common electrode CE, etc.The pixel switching element PSW is formed of, for example, a thin filmtransistor (TFT). The pixel switching element PSW is electricallyconnected to the gate line G and the source line S. The pixel switchingelement PSW may be either a top-gate TFT or a bottom-gate TFT. Further,although a semiconductor layer of the pixel switching element PSW isformed of, for example, polysilicon, it may be formed of amorphoussilicon.

The pixel electrode PE is electrically connected to the pixel switchingelement PSW. The pixel electrode PE is opposed to the common electrodeCE via an insulating film. The common electrode CE, the insulating film,and the pixel electrode PE form a storage capacitor CS. When a pixelsignal is written to the storage capacitor CS, spatial light modulationof liquid crystal LQ between the pixel electrode PE and the commonelectrode CE is realized according to the voltage.

FIG. 5 shows, in particular, a block configuration example inside theliquid crystal driver IC1, which is an IC chip.

Video data from the application processor HOS is input to a video memory202 via an interface receiver 201. The video data read from the videomemory 202 is latched in a line latch circuit 203. The line latchcircuit 203 can latch video data of one line or a plurality lines of theliquid crystal display panel LCD.

The video data corresponding to each pixel which has been read from theline latch circuit 203 is subjected to digital-to-analog conversion by asource amplifier 204, and becomes a pixel signal by performing gammacorrection, etc., by amplification. The pixel signal obtained in thisway is written to a pixel (a display element) of the liquid crystaldisplay panel LCD. More specifically, the pixel signal is written to thestorage capacitor CS shown in FIG. 4.

Blocks of the video memory 202, the line latch circuit 203, the sourceamplifier 204, etc., as a whole may be called a video data processingunit 241. The pixel signal generated in the video data processing unit241 is input to a display element array unit 240 a. The display elementarray unit 240 a is integrated with a touch detection element array unit240 b.

Meanwhile, a synchronization signal, a command, etc., from theapplication processor HOS is retrieved by means of the interfacereceiver 201. The synchronization signal and the like retrieved by theinterface receiver 201 is input to a timing controller 213.

The timing controller 213 can set an operation mode and an operatingsequence of the liquid crystal driver IC1 or switch the operation modein accordance with the command. The operation mode includes periods suchas a write period in which the pixel signal is written to a pixel ofeach horizontal line, a pixel display period, and a touch detectionperiod (a non-display period).

The timing controller 213 generates various timing pulses to realize theaforementioned sequence, on the basis of an internal clock from anoscillator 214.

Note that the interface receiver 201 converts an external clock rate ofdigital data sent from the application processor HOS into an internalclock rate for the internal digital data. For example, a write operationof the interface receiver 201 synchronizes with the external clock, anda read operation synchronizes with the internal clock.

The timing controller 213 can refer to external horizontalsynchronization signal HSYNC from the interface receiver 201 andsynchronize with external horizontal synchronization signal HSYNC.

Various timing pulses for display of the timing controller 213 are inputto the video memory 202, the line latch circuit 203, the sourceamplifier 204, and a panel control signal generation unit 220. Further,various timing pulses for a sensor of the timing controller 213 areinput to a touch detection element control signal generation unit 231and a touch interface 232.

The panel control signal generation unit 220 generates a driving signalfor the gate circuit GD and the common electrode driving circuit CD, andrealizes video display of the liquid crystal display panel LCD. Thetouch detection element control signal generation unit 231 generates theso-called touch detection driving signal for driving the sensor SE.

In this way, the liquid crystal driver ICI can set a write period withrespect to a pixel and a touch detection period in the liquid crystaldisplay panel LCD.

The touch interface 232 receives detection signal Rxs from the detectionelement Rx, and hands it over to the touchpanel controller IC2. Thetouchpanel controller IC2 determines the position on the display surfacethat is being touched by the user's finger or a stylus by usingdetection signal Rxs from the detection element Rx.

Note that the detection element Rx can be formed by using, for example,indium-tin-oxide (ITO), which is transparent.

In the above structure, blocks of the panel control signal generationunit 220, the touch detection element control signal generation unit231, the timing controller 213, the oscillator 214, etc., as a whole maybe called a scan driving unit 242. Accordingly, the scan driving unit242 comprises a second clock generation unit (the oscillator 214), and apixel signal and a display driving signal can be sequentially suppliedto display elements in a time-sharing manner in synchronization with aclock of the second clock generation unit 214, thereby performingdisplay scanning. Further, the scan driving unit 242 supplies the touchdetection driving signal to a touch detection element.

Also, in the above structure, blocks of the touch interface 232, thetouchpanel controller IC2, etc., may be called a touch detection unit243. The touch detection unit 243 can perform touch detection bysampling a detection output based on a touch detection element. By thisoperation, it is determined which part of the display surface is beingtouched by the user's finger or the stylus.

The liquid crystal driver IC1 comprises a regulator 251 and a boostercircuit (a charge pump) 252 as a power supply unit of an internalcircuit. The regulator 251 receives power supply from the battery BATT,as shown in FIG. 6A, for example, and generates a drive voltage by anoutput amplifier 251A and outputs the drive voltage stably. Here,potential voltages in two levels are retrieved from the battery BATT andselectively input by a selector switch 251B on the basis of a controlinstruction, so that the drive voltage can be controlled stepwise. Thisdrive voltage is transmitted to the interface receiver 201, the videomemory 202, the line latch circuit 203, the timing controller 213, andthe oscillator 214. The booster circuit 252 is structured by, forexample, a DC-to-DC converter. With the drive voltage in question, aboost frequency is controlled in receipt of power supply from theregulator 251 as shown in FIG. 6B, thereby boosting a direct-currentvoltage to a predetermined level and the boosted voltage is output tothe source amplifier 204, the panel control signal generation unit 220,and the touch detection element control signal generation unit 231.Consequently, individual circuit blocks are operated appropriatelyinside the liquid crystal driver IC1.

Here, in the display device according to the above-described structure,a touch sensor is operated in a blanking period of liquid crystaldriving. In the display device according to the present embodiment,while all of the common electrodes are fixed at a predetermined voltagein the display period and a signal is sequentially supplied to eachpixel through each of the gate lines and source lines, in the blankingperiod, a signal is sequentially supplied only to a common electrodewhich contributes to touch detection. Accordingly, a panel driving loadin a display driving period (the display period) is remarkably greaterthan that in a sensing operation period (the touch detection period) ofthe touch sensor. Accordingly, because of a periodic load variation inthe display period and the touch detection period, the regulator 251 andthe booster circuit 252 for the liquid crystal driving cannot catch upwith the load variation, and thus, a ripple occurs in the power supplyvoltage. The ripple may produce noise due to vibration of components.

Hence, in the embodiment, one of or both of the regulator 251 and thebooster circuit 252 are controlled dynamically in periods in whichdifferent loads are applied. With this control, a power control signalis generated by the timing controller 213, and output to the regulator251 and the booster circuit 252. The regulator 251 and the boostercircuit 252 control a drive voltage to an output destination on thebasis of the power control signal, and perform mitigation driving so asto mitigate a difference between electrical loads.

More specifically, as shown in FIG. 7, the timing controller 213comprises a display period generation unit 213 a, a touch detectionperiod generation unit 213 b, a sequencer 213 c, and a power controlunit 213 d. By the instruction from the sequencer 213 c, the displayperiod generation unit 213 a sends a control signal to the video dataprocessing unit 241 and the panel control signal generation unit 220 sothat a predetermined period is treated as a video display period. Also,by the instruction from the sequencer 213 c, the touch detection periodgeneration unit 213 b sends a control signal to the touch detectionelement control signal generation unit 231 and the touch interface 232so that a predetermined period is treated as a touch detection period.Further, the power control unit 213 d discriminates between the displayperiod and the touch detection period by the instruction from thesequencer 213 c, and generates control signals for setting drivevoltages of their respective periods and sends them to the regulator 251and the booster circuit 252 so as to reduce load variation.

First Embodiment

Referring to FIG. 8, and (a) to (d) of FIG. 9, a first embodiment forreducing the load variation will be described. In the first embodiment,it is assumed that the booster circuit (the charge pump) is stoppeddynamically or a boost frequency is changed in periods in whichdifferent loads are applied. FIG. 8 is a flowchart showing the specificsof control of the first embodiment which is processed by the sequencer213 c, and FIG. 9 is a timing chart indicating the specifics of controlof FIG. 8.

First, when the display device is powered on, setting of the displayperiod and the touch detection period is performed (step S11). When thedisplay period starts, the booster circuit 252 is powered on or thefrequency is set to a first boost frequency for display driving (stepsS12 and S13). Next, when the touch detection period starts, the boostercircuit 252 is powered off or the frequency is set to a second boostfrequency for display stopping (steps S14 and S15). Then, the processingof steps S12 to S15 is repeated until completion of the control isinstructed by the power-off (step S16), and when the completion of thecontrol is instructed, a series of operation is completed.

Illustrations (a) to (d) of FIG. 9 indicate this state. Illustration (a)of FIG. 9 shows the state of power variation in load period A (displayperiod) and load period B (touch detection period). Further, (b) of FIG.9 shows that no control is performed in either load period A (displayperiod) or load period B (touch detection period). In this case, asshown by a one-dot chain line, the power output changes greatlyperiodically in (a) of FIG. 9. In contrast, as shown in (c) of FIG. 9,in the present embodiment, the voltage is set to a boosted voltage undernormal conditions in a display period of load period A, and stops aboosted output in a touch detection period of load period B.Alternatively, as shown in (d) of FIG. 9, the frequency is set to aboost frequency (the first boost frequency) under normal conditions in adisplay period of load period A, and set to the second boost frequencywhich is lower than the first boost frequency in a touch detectionperiod of load period B. Variation in the power source voltage whichoccurs in load periods A and B can thereby be sufficiently suppressed asshown by a solid line in (a) of FIG. 9.

Second Embodiment

Referring to FIG. 10, and (a) to (d) of FIG. 11, a second embodiment forreducing the load variation will be described. In the second embodiment,when the regulator 251 or the booster circuit 252 is provided with afeedback circuit, it is assumed that a reference potential is changeddynamically. FIG. 10 is a flowchart showing the specifics of control ofthe second embodiment which is processed by the sequencer 213 c, andFIG. 11 is a timing chart indicating the specifics of control of FIG.10.

First, when the display device is powered on, setting of the displayperiod and the touch detection period is performed (step S21). When thedisplay period starts, the reference potential of the booster circuit252 is set to a first voltage level specified for the display period(steps S22 and S23). Next, when the touch detection period starts, thereference potential of the booster circuit 252 is set to a secondvoltage level which is lower than the first voltage level (steps S24 andS25). Then, the processing of steps S22 to S25 is repeated untilcompletion of the control is instructed by the power-off (step S26), andwhen the completion of the control is instructed, a series of operationis completed.

Illustrations (a) to (d) of FIG. 11 indicate this state. Illustration(a) of FIG. 11 shows the state of power variation in load period A(display period) and load period B (touch detection period). Further,(b) of FIG. 11 shows that no control is performed in either load periodA (display period) or load period B (touch detection period). In thiscase, as shown by a one-dot chain line, the power output changes greatlyperiodically in (a) of FIG. 11. In contrast, as shown in (c) of FIG. 11,in the present embodiment, the reference potential of the boostercircuit 252 is set to the first voltage level under normal conditions inthe display period, in the display period of load period A, and is setto the second voltage level which is lower than the first voltage levelin the touch detection period of load period B. Variation in the powersource voltage which occurs in load periods A and B can thereby besufficiently suppressed as shown by a solid line in (a) of FIG. 11.

Although the case of controlling the reference potential of the boostercircuit 252 has been described for the above embodiment, the referencepotential of the regulator 251 may be controlled. That is, as shown in(d) of FIG. 11, a similar advantage can be obtained even by setting thereference potential of the regulator 251 to the first voltage level inthe display period of load period A, and setting the reference potentialof the regulator 251 to the second voltage level which is lower than thefirst voltage level in the touch detection period of load period B. As amatter of course, the regulator 251 and the booster circuit 252 may becontrolled together.

Third Embodiment

In both of the first and the second embodiments, display period A andtouch detection period B are fixed. However, a load may be changedgreatly for each of the switching of the periods, which may affect aresponse or image quality. This is noticeable at the time of boostswitching of the booster circuit 252. Hence, in the third embodiment,considering the influence on the response and image quality, the boostswitching timing at a load variation border is to be controlled. FIG. 12is a flowchart showing the specifics of control of the third embodimentwhich is processed by the sequencer 213 c, and FIG. 13 is a timing chartindicating the specifics of control of FIG. 12.

First, when the display device is powered on, display period A and touchdetection period B are set as standard, as shown in (a) of FIG. 13, andtime t for shifting the timing of an end of touch detection period B,that is, the timing of a start of display period A, is set, as shown in(b) of FIG. 13 (step S31). When display period A is started, voltageboost is performed or the frequency is set to the first boost frequency(steps S32 and S33), and a lapse of display period A is monitored by,for example, a count of a clock, to determine the ending of displayperiod A (step S34). When the ending of display period A is detected,touch detection period B is started and the voltage boost is stopped orthe frequency is set to the second boost frequency (steps S35 and S36),and a lapse of touch detection period B is monitored by, for example, acount of the clock in accordance with shift time t, to determine theending of touch detection period B (step S37). Then, the processing ofsteps S32 to S37 is repeated until completion of the control isinstructed by the power-off (step S38), and when the completion of thecontrol is instructed, a series of operation is completed.

According to the above processing, as shown in (b) of FIG. 13, displaycan be started earlier by time t than display period A which is set asstandard. That is, voltage boost is executed when a period is switchedfrom the non-display period to the display period. More specifically,when a period is shifted from touch detection period (non-displayperiod) B to display period A, as shown in (a) of FIG. 13, a frequencyat the time of display period is input at the time of touch detectionperiod (non-display period) B, as shown in (b) of FIG. 13, prior to thestart of subsequent display period A by time t (where t is a shift timeof starting the voltage boost), thereby executing pre-charge.Consequently, display carried out in subsequent display period A isoperated smoothly from the start. In this way, it becomes possible tomitigate a sudden load variation.

While the above-mentioned shift time t may be fixed, it may be changedrandomly or periodically. Further, not only when a period is shiftedfrom touch detection period (non-display period) B to display period A,but also when a period is switched from display period A to touchdetection period B, the timing of voltage boost may be controlled.

Fourth Embodiment

In the third embodiment described above, considering the impact on theresponse and image quality caused by the load being varied greatly foreach of the switching of the display period and the touch detectionperiod, the boost switching timing at a load variation border iscontrolled. In a fourth embodiment to be described below, in the case ofa low-temperature polysilicon (LTPS) display panel, in the touchdetection period (the non-display period), an LTPS driving signal issubjected to modulation control at the time of switching between thenon-display and display periods, thereby reducing an abrupt loadvariation. FIG. 14 is a flowchart showing the specifics of control ofthe fourth embodiment which is processed by the sequencer 213 c, andFIG. 15 is a timing chart indicating the specifics of control of FIG.14. Here, a pulse width modulation whereby a pulse width of a 1Hhorizontal period is variable is adopted for the LTPS driving signal,and it is assumed that the modulation is performed at a duty ratio of20% in the display period, and a duty ratio of 100% in the touchdetection period. A modulated waveform of a conventional LTPS drivingsignal is shown in (a) of FIG. 15, and a change in panel load at thattime is shown in (b) of FIG. 15. As can be seen, with a conventionalmethod, a sudden load variation occurs at a border between the displayperiod and the touch detection period.

In contrast, in the fourth embodiment, when the display device ispowered on, the display period and the touch detection period are set asstandard, as shown in (a) of FIG. 15, and also, a predetermined timefrom the start of the touch detection period (hereinafter referred to asan “IN period”) and a predetermined time before the end of the touchdetection period (hereinafter referred to as an “OUT period”) are set,respectively (step S41). When the display period is started, the dutyratio is set at 20% (steps S42 and S43), and a lapse of the displayperiod is monitored by, for example, a count of a clock, to determinethe ending of the display period (step S44). When the ending of thedisplay period is detected, after the touch detection period has beenstarted, the duty ratio is continuously increased from 20 to 100% withinthe IN period (step S45). Next, a lapse of the touch detection period ismonitored by, for example, a count of the clock, and the duty ratio iscontinuously reduced from 100 to 20% within the OUT period of the touchdetection period (step S46). Then, the processing of steps S42 to S46 isrepeated until completion of the control is instructed by the power-off(step S47), and when the completion of the control is instructed, aseries of operation is completed.

Note that the rate or degree of change when the duty ratio between thetouch detection period and the display period is changed sequentially isnot limited to the above, and a value according to the performance ofthe display device or the performance of the IC, etc., can be adopted.

According to the above structure, with respect to the LTPS drivingsignal, the duty ratio is continuously increased from 20 to 100% withinthe IN period of the touch detection period, and the duty ratio iscontinuously reduced from 100 to 20% in the OUT period, as shown in (c)of FIG. 15. In this way, the panel load is gradually increased orreduced in the IN period and the OUT period of the touch detectionperiod, as shown in (d) of FIG. 15, and a sudden load variation can beprevented.

Further, in the fourth embodiment described above, although it has beendescribed that the pulse width modulation is adopted for the LTPSdriving signal, the modulation is not limited to the above. That is,even if frequency modulation is adopted, the embodiment can beimplemented similarly. In the case of frequency modulation, thefrequency should be set in such a way that a first frequency is adoptedin a 1H horizontal period of the display period, a second frequency isadopted in a 1H horizontal period of the touch detection period, thefirst frequency is raised or lowered to the second frequency in an INperiod of a touch horizontal period, and the second frequency is raisedor lowered to the first frequency in an OUT period.

Other Embodiment

In the second to fourth embodiments described above, the lengths of thedisplay period and the touch detection period (the non-display period)are changed every time. In this way, since a ripple of a power sourcevoltage caused by the periodicity of each period is reduced, it becomespossible to reduce the load variation.

Also, in each of the above embodiments, since a period of detecting atouch by a finger (i.e., the touch detection period which involves afinger) has been described as an example of the non-display period, theother forms of the non-display period include a period of detecting atouch by an active stylus, an optical detection period using a scannerdisplay, a period of detecting that an ear is close using a proximitysensor, etc. Further, for a security purpose, for example, theembodiment may also be applied to an application which assumes aproximity detection period using a proximity sensor to be a non-displayperiod and performs face detection processing of a proximal object (aperson) by a camera.

While certain embodiments have been described, these embodiments havebeen presented by way of example only, and are not intended to limit thescope of the inventions. Indeed, the novel embodiments described hereinmay be embodied in a variety of other forms; furthermore, variousomissions, substitutions and changes in the form of the embodimentsdescribed herein may be made without departing from the spirit of theinventions. The accompanying claims and their equivalents are intendedto cover such forms or modifications as would fall within the scope andspirit of the inventions.

It should be understood that various changes and modifications to thepresently preferred embodiments described herein will be apparent tothose skilled in the art. Such changes and modifications can be madewithout departing from the spirit and scope of the present subjectmatter and without diminishing its intended advantages. It is thereforeintended that such changes and modifications be covered by the appendedclaims.

1-14 (canceled)
 15. A display device comprising: a display panelconfigured to display an image; and a display driver configured to drivethe display panel, the display driver comprising: a video signalprocessor configured to convert a video signal for the image to a pixelsignal, to supply the pixel signal to the display panel, to selectivelydrive the display panel in a display state in which the image isdisplayed and a non-display state in which the image is not displayed,and including a source amplifier configured to amplify the pixel signal;a power supply device configured to supply drive power to the videosignal processor, and including a booster circuit configured to boost avoltage of the drive power to the source amplifier; and a controllerconfigured to control the video signal processor and the power supplydevice, wherein the controller instructs a display period driven in thedisplay state and a non-display period driven in the non-display state,and instructs off-state driving configured to stop boosting the voltageof the drive power to be output to the source amplifier when the displayperiod is switched to the non-display period.
 16. The display device ofclaim 15, wherein the controller instructs on-state driving configuredto activate boosting the voltage of the drive power to be output to thesource amplifier when the non-display period is switched to the displayperiod.
 17. The display device of claim 15, wherein the video signalprocessor comprises: an interface receiver configured to convert anexternal clock rate of the video signal into an internal clock rate; anda line latch circuit configured to latch the video signal of one line ora plurality of lines of the display panel.
 18. The display device ofclaim 15, wherein the power supply device includes a regulatorconfigured to: receive power supply; generate the drive power from thepower supply; and output the drive power stably.
 19. The display deviceof claim 15, wherein the display panel includes a plurality of pixelelectrodes and a plurality of common electrodes for forming a storagecapacitor and performing spatial light modulation for each pixel basedon the pixel signal, and the video signal processor supplies the pixelsignal to the pixel electrodes in the display period, and does notsupply the pixel signal to the pixel electrodes in the non-displayperiod.
 20. The display device of claim 15, wherein the video signalprocessor further comprises a common electrode driving circuitconfigured to drive the common electrodes, the common electrode drivingcircuit sets all of the common electrodes at a common potential in thedisplay period and sets some of the common electrodes at a potentialother than the common potential in the non-display period.
 21. Thedisplay device of claim 20, further comprising; a plurality of touchdetection elements configured to detect a touch operation from a changein capacitance based on the potential between the touch detectionelements and some of the common electrodes in the non-display period,and a touch-panel controller connected the touch detection elements andconfigured to receive detection output of the touch detection elements.22. An integrated circuit device for driving a display panel configuredto display an image, the device comprising: a video signal processorconfigured to convert a video signal for the image to a pixel signal, tosupply the pixel signal to the display panel, to selectively drive thedisplay panel in a display state in which the image is displayed and anon-display state in which the image is not displayed, and including asource amplifier configured to amplify the pixel signal; a power supplydevice configured to supply drive power to the video signal processor,and including a booster circuit configured to boost a voltage of thedrive power to the source amplifier; and a controller configured tocontrol the video signal processor and the power supply device, whereinthe controller instructs a display period driven in the display stateand a non-display period driven in the non-display state, and instructsoff-state driving configured to stop boosting the voltage of the drivepower to be output to the source amplifier when the display period isswitched to the non-display period.
 23. The integrated circuit device ofclaim 22, wherein the controller instructs on-state driving configuredto activate boosting the voltage of the drive power to be output to thesource amplifier when the non-display period is switched to the displayperiod.